National Park Scouts

Into the Dark: The Hidden Caves of Sequoia

Host: Jenni · Topic: Sequoia's 240 caves, cave adaptation, Illacme tobini

Intro

Most people who visit Sequoia National Park spend their whole trip looking up. And honestly, that's fair. The trees are enormous. But here is a fact that almost nobody knows about this park. There are 240 caves underneath it. 240 caves, under this park, right now. And almost nobody knows they're there. Today we're going into the dark. Let's go.

Welcome to National Park Scouts, the show where curious kids discover America's wildest places. I'm Jenni. We are back at Sequoia National Park, which sits right next door to Kings Canyon National Park. The two parks share a border and are actually managed together by the National Park Service, so you'll often see them listed as Sequoia and Kings Canyon. For this series, we're focused on Sequoia. But that shared border matters today, because the cave system underneath these parks runs through both of them.

Last episode, we looked at the biggest tree on Earth, General Sherman. Today we're going in the opposite direction; down, down into the dark, into the cold, into 240 caves right underneath the giant sequoias, and the creatures living in them that science is still trying to figure out.

How the caves formed

How does that even happen? It starts with the rock. Underneath Sequoia, a lot of the rock is marble; the same fancy stone used in fancy buildings. Marble is also what forms when limestone gets crushed and heated deep underground by enormous pressure, the same forces that pushed the Sierra Nevada mountains up and out of the earth millions of years ago.

And here's the thing about marble: water can slowly dissolve it. Over millions of years, slightly acidic water, think of it like extremely, extremely weak lemon juice, seeped down through tiny cracks in the rock and dissolved it, molecule by molecule. It carved tunnels, it hollowed out rooms, it made passages that go on for miles. That's a very slow process; we're talking millions of years to build one cave system.

Crystal Cave

The only cave you can actually walk into as a visitor is called Crystal Cave. It was discovered in 1918, but not by scientists; it was discovered by two park employees who were fishing nearby and noticed the creek they were following just disappeared underground. They followed it in.

Inside Crystal Cave, it's 48 degrees all year, no matter what. July heat wave outside, 48 degrees. December snowstorm, 48 degrees. It is always, always 48 degrees in there. Bring a jacket.

Inside you'll see stalactites hanging from the ceiling like stone icicles, and stalagmites growing up from the floor. Here's the trick to remember which is which: stalactites have to hold on tight to the ceiling; stalagmites might one day reach the top. Some of those formations have been growing for tens of thousands of years, at a rate of one cubic inch per hundred years. They are in no hurry at all.

Crystal Cave is the one open to visitors. The other 239, they're locked; off limits; you need a permit. And that's where it gets really interesting, because scientists have found some surprises inside of them.

Park Sound

Guess That Park Sound

Okay, scouts, it's time for guess that park sound. Let's listen in. Where do you think that sound is coming from? Take your best guess. We'll come back to it right after the break.

This episode of National Park Scouts is made possible by our listeners. Stick around; we're right back after this.

Answer

Was that one too easy? That's the sound of water dripping inside a cave, deep underground. Here's the thing about those drips: every single one is carrying a tiny speck of dissolved mineral. When the water drips and evaporates, it's leaving that speck behind. Drip, speck, drip, speck. Over thousands of years, those tiny little specks stack up, and that's how stalactites grow. That sound you just heard is the cave being built right now, one drop at a time. And it's been doing that since before General Sherman was a seedling.

Life in total darkness

When animals live in total darkness for thousands and thousands of generations, they start to change. Eyes become smaller, then they disappear completely; there's no light, so why spend energy building eyes? Skin color fades; no sun means no need for protection from the sun. Animals that would normally be brown or tan become completely pale, almost see-through.

But here's the trade-off. What those animals lose in one place, they gain somewhere else. Legs and antennae grow much longer, so they can feel the world instead of seeing it. And the tiny hairs covering their bodies become incredibly sensitive to changes in air movement; they can feel you coming before you get anywhere near them, in total darkness, without eyes.

Scientists sometimes call it losing what you don't need and gaining what you do. It's not going backwards; it's the animal becoming perfectly built for exactly one place: a dark, cold, underground marble cave. And once something adapts to that, it exists nowhere else on Earth.

A team of biologists spent years carefully surveying caves right here in Sequoia and Kings Canyon. They thought they might find a handful of new species. They found more than 30 animals that had never been seen by scientists before, ever, anywhere: eyeless spiders, blind beetles, pale little shrimp-like creatures living in underground streams that have never seen sunlight, and a pseudoscorpion that looks like a tiny scorpion with two big claws but no stinging tail. One researcher called it "the lion of the cave"; pale, armed, and completely in charge.

These creatures have been living under the sequoia trees, in the dark, in the silence, for probably thousands of years. And for almost all of that time, nobody on the surface had any idea they existed.

The millipede discovery

In October of 2006, a cave biologist named Jean Krejca was exploring one of Sequoia's off-limits research caves, a place called Lange Cave. And she turned over a rock. Underneath it was something nobody had ever seen: a millipede, as thin as a piece of thread, about as long as a grape, completely pale white, no eyes, and 414 legs.

That is so many legs on a tiny, tiny animal. To give you a sense of that: you have two legs, a spider has eight, a regular centipede has somewhere around 40. 414 is a genuinely hard amount of legs to picture.

Scientists named it Illacme tobini. And here's where it gets even more interesting: it has about 200 poison glands in its body, it releases silk from tiny hairs all over its skin, and it almost certainly eats fungus growing directly on cave rock. It may only exist in this cave, or a tiny handful of caves nearby; scientists aren't sure, because here's the thing: they've only ever found one.

After Jean Krejca's discovery, researchers went back and searched 63 other locations across the Sierra Nevada foothills, every cave they could reach. They didn't find a single additional Illacme tobini. So the one she found is the only one they've ever studied.

This creature has been living under Sequoia National Park in total darkness, completely unknown to anyone. It was there when General Sherman was already ancient. It was there when the first people ever walked through this valley. Nobody knew it existed until a scientist turned over one rock. What else is down there? Nobody knows yet.

Wildcard

Who Would Win: Cave Creature Showdown

Three of Sequoia's strangest cave animals, only one ultimate cave survivor. You get to choose.

Contestant one: the cave spider. No eyes, spins webs in total darkness, has hairs on every leg so sensitive they can feel air moving before you get anywhere close. Completely unbothered.

Contestant two: the cave pseudoscorpion. Two big claws that inject venom. Pale white. Scientists literally called it the lion of the cave. Terrifying at its actual size of half an inch.

Contestant three: Illacme tobini. 414 legs, 200 poison glands, makes its own silk, eats fungus off rocks, no eyes. Has been living in total darkness since the ice age. Scientists have found exactly one.

Who do you think would win? Jenni's pick: the pseudoscorpion. As cool as the millipede is, how can you win over something that has claws that inject venom? What do you think wins?

No scripted joke segment appears in this transcript, unlike prior episodes; omitted rather than invented.

Scout Question of the Day

This week's question: Do you like caves? Would you go in one?

Ellie, age 9: "I would like to go inside the cave because it would be a fun adventure, and I would like to see what's inside."

Quinn, age 12: "I would rather stay outside and look at the trees because trees are more fascinating, and because outside it's more sunny; in the cave, it's dark and gloomy."

I love hearing from you. Do you have a question about a national park, or do you want to be on this podcast? Visit nationalparkscouts.com/contact. While you're there, check out our coloring pages, word searches, and bingo cards, and subscribe to find out which park we visit next.

Scout Mission

Your Mission

If you're at home: turn off every light in a room and cover any device that glows too. Sit in total darkness for two minutes. Then ask yourself: if I lived my whole life like this, what would I start using instead of my eyes?

If you're at Sequoia National Park: book a guided tour of Crystal Cave. You can't buy tickets at the cave; you have to reserve ahead through Sequoia Parks Conservancy. Bring a jacket, it's 48 degrees in there, always. And when you're inside, watch the tip of a stalactite; if conditions are right, you might see a drop forming. That's the cave building itself right in front of you.

Outro

What did you learn today that most adults don't know? I learned that there are 240 caves underneath Sequoia National Park. While everyone else is looking up, there's also interesting things happening underground. Who knows what else is down there?

Thanks for joining us today, scouts. Next episode, we're coming all the way back up to the high Sierra to meet a tiny frog that nearly vanished from California's mountains forever, and find out how scientists are bringing it back, one helicopter at a time.